Last night’s winner shed 60 percent of her starting weight. Find out how much is too much when it comes to weight loss

Last night, the winner of The Biggest Loser was revealed. Rachel Frederickson went from 260 pounds to 105 pounds—and she’s only 5’4”. That means that she lost a whopping 60 percent of her body weight—crazy, right?! But fans on Twitter actually weren’t so happy for her. They said that she looked really unhealthy, and Frederickson’s trainers were even surprised by her massive slim down.

First, it's worth noting right off the bat: It's almost always impossible to tell if someone is healthy or not just by looking at them. That being said, dropping such an enormous amount of weight over the course of a five-month season is certainly shocking. So here’s the ultimate, and more leigitimate, question: Is it ever safe to lose 60 percent of your body weight, like Frederickson did? In short, it depends. “It definitely can be—if you have 60 percent of your body weight to lose,” says Keri Glassman, R.D. a weight-loss expert for Women’s Health. “If a short 300-pound guy lost 60 percent of his body weight, for example, chances are, he would be fine. But in Frederickson’s situation, her slim-down is probably not safe because losing 60 percent of her weight puts her below her ideal body weight, according to BMI charts.” Granted, BMI isn’t a perfect measure of what your ideal body weight should be—but it does give you a helpful ballpark to start out with.

Frederickson's underweight BMI aside, there’s another big issue here: how quickly she dropped the pounds. Frederickson lost 155 pounds over five months, which means she lost around a pound a day—sometimes more. If you're losing that much weight that quickly, it means you’re eating at such a calorie deficit that it becomes really difficult to get all the nutrients you need to maintain healthy functioning.

Not to mention, you’re also setting yourself up to regain those lost pounds. “If you lose weight very fast, you’re more likely to set yourself up for yo-yo dieting because you're likely doing things that are extreme and aren't sustainable in the long run,” says Glassman. Not that Frederickson should necessarily take all of the fire here; The Biggest Loser has been criticized in the past for encouraging weight loss that isn't sustainable or even necessarily healthy, given the relatively short time span of each season, and this is an example that critics say exemplifies that.

So how quickly is it safe for you to lose if you’re trying to drop pounds? “The general consensus is that healthy weight loss is about two pounds a week, but it can certainly be more depending on how much weight the person has to lose," says Glassman. For more info on how to drop pounds in a healthy way, visit our weight-loss channel.